1. Field of Invention
The invention relates to a liquid quenching system for use with continuous furnaces for heat treating small parts. In particular, the invention relates to a bearing, rotatable joint and protection member and the method of their use in conjunction with a rotary quenching drum of the liquid quenching system.
2. Description of Related Art
Continuous heat treating furnaces such as conveyor belt, shaker hearth, shuffle hearth or rotary retort furnaces are often used to heat treat large quantities of relatively small parts, such as screws, nuts, washers, bolts and pins. The handling of such small parts, particularly during the quenching process, has long presented many different problems.
A first problem involves the metallurgical requirements for a thorough quench of each small part. Another problem includes the practical economic requirements for recovery of the quenched pieces. Installation and maintenance of the quenching apparatus is itself problematic, and the need to minimize both the initial quantity of quenchant required and the loss of quenchant during use also present serious problems. Finally, in rotary quenching drum type liquid quenching systems, a problem exists wherein the small parts become lodged in the bearing and seals that seal the rotary quenching drum in rotational relationship with respect to the quench chute that discharges the small parts into the rotary quenching drum.
It has long been the practice in the conventional art to include pit type quench systems, such as those shown in U.S. Pat. No. 3,531,096 to Krach et al. and U.S. Pat. No. 3,650,853 to Keough for use in connection with furnaces of the conveyor belt, shaker hearth and shuffle hearth varieties. The disadvantages of such pit type quench systems have been appreciated. A system designed to overcome these disadvantages is disclosed in U.S. Pat. No. 4,036,478 to Smith et al., which is incorporated herein by reference. However, the liquid quenching system disclosed in the '478 patent suffers from many additional and different problems. In particular, parts being transferred from a transfer chute to the rotary quenching drum of the '478 patent sometimes become lodged in the seal between the transfer chute and the rotary quenching drum. As a result, the transfer chute and its seal can become damaged and scored, and sometimes the parts will make their way entirely through the seal and fall into the main quenching tank in which the rotary quenching drum is located. When a part falls into the quenching tank, the part will often be drawn into the recirculating system and will either clog the quenchant lines or jam the pump impeller or valving disposed inside of the quenchant lines.
Besides scoring the transfer chute, the parts that become lodged in the seal between the rotary quenching drum and transfer chute can potentially cause the rotary quenching drum to stop rotating and lock up.
The structure of the '478 patent does not facilitate quick and easy repair of the rotatable joint, which includes a bearing and seal between the rotary quenching drum and transfer chute, once the joint has become worn or damaged by stray parts. In addition, the location of the seal and bearing requires that they always be submerged in quenchant, which greatly accelerates their deterioration and ultimate need for repair. Accordingly, the seal between the drum and transfer chute must be replaced frequently because of damage caused by metal parts being caught between the seal and bearing, or through accelerated wear from being submerged in quenchant.
Thus, the industry lacks an apparatus and method for extending the operational life of the rotatable joint between the transfer drum and the transfer chute.